I'm in the process of breaking in a Thunder Tiger f.75s. When running it, it seems that there is some fuel/oil seeping out from under the valve cover. Is this normal or bad?

Thanks.

Neither. It's merely indicative that your valve cover is probably loose and simply needs to be tightened. Thunder Tiger makes wonderful glow engines, both two cycle and four cycle. Your F-75s is their latest design and is, by all accounts, a terrific running engine.